1. Field of the Invention
The present invention relates to a liquid developer for use in electrophotography which is prepared by dispersing a toner consisting essentially of a pigment or dye and a nonaqueous dispersed resin uniformly in a carrier liquid having a high insulating property and a low dielectric constant.
2. Description of the Prior Art
The conventional liquid developers for use in electrophotography are prepared by dispersing, in a carrier liquid having a high insulating property and a low dielectric constant such as a petroleum aliphatic hydrocarbon, a toner consisting essentially of a pigment such as carbon black or dye and a synthetic or natural resin such as acrylic resin, phenol-denaturated alkyd resin, Staybelite resin, polymerized resin, synthetic rubber or the like and further added with a polarity controlling agent such as lecithin, metallic soap, linseed oil, higher fatty acid or the like. In the brand-new conventional liquid developer, the resin comprising the toner is adsorbed onto the pigment or dye and consequently the toner is permitted to hold a distinct positive or negative polarity as well as maintain a uniform dispersion stability. And, this toner causes electrophoresis according to the charge pattern of an electrostatic latent image formed on the surface of a photosensitive element during its developing step to thereby fix to the charge pattern and form an image thereon. However, such conventional liquid developers are defective in that because the resin and/or the polarity controlling agent diffuse and dissolve in the carrier liquid gradually with the lapse of time, the polarity becomes indistinct and ultimately aggregation takes place in the developer, whereby the fixability is deteriorated and consequently copied images are poor in sharpness. Still further, such conventional developers, once the toners used have aggregated, are utterly impossible to reuse, because it is impossible to re-disperse the aggregated toners.